Morphometric analysis of debris flows basins in the Eastern Rhodopes (Bulgaria) using geospatial technologies

Debris flows are considered as a rapid movement of highly water-saturated colluvial and proluvial deposits. Besides the intensive rainfall and snowmelt, there are several other factors—prerequisites to debris flows: morphometric characteristics, rocks composition, active tectonics and deforestation. The current research is directed to the analysis of morphometric parameters of debris flow areas located in Eastern Rhodopes (Bulgaria). Two types of debris flows are analysed—gully-induced debris flows and stream torrent section with debris flood occurrence. The aim is to determine morphometric indicators to be used for discrimination of debris flow types and further susceptibility assessment. The following parameters are calculated: basin area and length, basin relief, relief ratio, Melton index, slope, topographic wetness index, stream power index and curvature. The analysis shows that slopes in a range 30–45° have most important role, among the other topographic factors, for debris flow initiation. Melton index is a meaningful indicator for discrimination of debris flow types. It is greater than 1 at gully-induced debris flows and much lower at the debris flood section (0.14–0.16). The analysis of curvature rasters, generated as a second derivative of digital elevation model (DEM), shows that the considered gullies are subject of intensive erosion and the process is still active. The research is elaborated in GIS environment on the basis of DEM and field investigations. Terrestrial laser scanning (TLS) of the low part of the basins and debris flow fan is done, and detailed terrain models are developed for the purpose of morphometric analyses.